The invention concerns a temperature-controlled wire holder that releases a wire under mechanical tension according to temperature.
In the field of space travel, a method is known (DE-A1-196 49 739) to secure the bent end of a wire under tension using a fusible link that melts when current is passed through it, thus releasing the wire. The fusible wire under tension (shaped as a coil) holds two halves of a two-part pin bracket together. When the wire is released, the two halves of the pin bracket separate under spring tension, releasing the pin from the bracket. Such pins may be used, for example, to hold solar panels in a collapsed state during rocket launch that are later freed by the release of the pin upon achievement of the mission goal. The use of a fusible link has the disadvantage of uncontrolled and undefined release.
From U.S. Pat. No. 4,487,465, a temperature-controlled wire holder made of shape memory material is known in which two free arms are mounted to a base by means of which a wire is held in an opening formed by the arms. The disadvantage of such a configuration is that the manufacturing process is extremely complex, and the temperature at which the arms open may be changed only by altering the shape memory alloy.
This task is solved by the invention by means of the characteristics of Patent claim 1. Additional embodiments of the invention are presented in the sub-claims.
The invention uses the characteristics of alloys that possess memory characteristics, so-called shape memory alloys based on TiNi alloys. Such alloys, for example, are known to possess two different solid phases, namely martensitic at low temperature and austenitic at high temperature, with a progressive phase transition as the alloy is heated.
The so-called xe2x80x9cone-way effectxe2x80x9d of such alloys is used to advantage. For this, a xe2x80x9cpseudo-plasticxe2x80x9d deformation of the martensite alloy is created that is known to re-form as austenite during temperature increase. Subsequent cooling into martensite, however, does not lead to further deformation, but rather the alloy remains in the condition characteristic of austenite.
The wire holder based on the invention has the advantage that it consists of fewer pieces, and may be incorporated into existing designs because of its compact design, thereby simplifying known installations with wire holders. A further advantage of the holder based on the invention consists in the fact that no pieces are broken loose or destroyed during the release of the wire, in contrast to pyrotechnical release processes. Using an application of shape memory alloys based on TiNi that have been pretreated using a special mechanical process, the austenite triggering temperature lies significantly above the values of commercially-available TiNi alloys. By the use of such alloys, wire holders based on the invention may be used in higher-temperature applications such as those encountered during space missions.